Microalgae Cultivation for Biofuels Production

By Abu Yousuf

Microalgae Cultivation for Biofuels Production explores the technological opportunities and challenges involved in producing economically competitive algal-derived biofuel. The book discusses efficient methods for cultivation, improvement of harvesting and lipid extraction techniques, optimization of conversion/production processes of fuels and co-products, the integration of microalgae biorefineries to several industries, environmental resilience by microalgae, and a techno-economic and lifecycle analysis of the production chain to gain maximum benefits from microalgae biorefineries.

• Provides an overview of the whole production chain of microalgal biofuels and other bioproducts
• Presents an analysis of the economic and sustainability aspects of the production chain
• Examines the integration of microalgae biorefineries into several industries

• Language: English
• Publisher: Academic Press
• Release date: Nov 23, 2019
• ISBN: 9780128175378

Book preview

Microalgae Cultivation for Biofuels Production

Editor

Abu Yousuf

Chemical Engineering & Polymer Science, Shahjalal University of Science and Technology, Sylhet, Bangladesh

Table of Contents

Cover image

Title page

Copyright

Dedicated to

List of Contributors

About the Editor

Preface

Acknowledgment

Chapter 1. Fundamentals of Microalgae Cultivation

Introduction

Fundamental Characteristics of Algae

Algae Mass Cultivation System

Algae Growth Factor

Traditional Sources of Biodiesel and Their Limitations

Microalgae as an Alternative

Conclusion and Recommendation

Chapter 2. Microalgae Cultivation Systems

Introduction

Growth Factor Affecting Microalgal Cultures

Metabolic Production Systems

Culture Systems

Concluding Remarks

Chapter 3. Microalgae Cultivation and Photobioreactor Design

Introduction

Nutrients Metabolisms

Three Cultivation Modes and Microalgal Components Synthesis

Design of Photobioreactors and Microalgae Harvesting Technologies

Conclusions

Chapter 4. Mixotrophic Cultivation: Biomass and Biochemical Biosynthesis for Biofuel Production

Introduction

Mixotrophic Microalgae Cultivation

Metabolisms of Mixotrophic Cultivation

Cultivation Parameters

Environmental Factors

Temperature

Nutrients Factor

Nitrogen Source

Activator and Inhibitors

Cultivation Mode

Biofuel Production Under Mixotrophic Cultivation Condition

Conclusion and Future Prospect

Chapter 5. Oleaginous Microalgae Cultivation for Biogas Upgrading and Phytoremediation of Wastewater

Introduction

Biogas Upgrading and Lipid production

Factors Affecting Biogas Upgrading and Lipid Production

Combining Biogas Upgrading and Wastewater Treatment

Recent Concepts for Microalgae Cultivation

Conclusions

Chapter 6. Efficient Harvesting of Microalgal biomass and Direct Conversion of Microalgal Lipids into Biodiesel

Introduction

Microalgal Biomass

Harvesting of Microalgal Biomass

Conversion of Microalgal Lipids Into Biodiesel

Conclusions

Chapter 7. Membrane Technology for Microalgae Harvesting

Introduction

Pressure-Driven Membrane Process

Osmotically Driven Membranes

Membrane Fouling Control

Future Prospect of Membrane Technology

Chapter 8. Processing of Microalgae to Biofuels

Introduction

Harvesting and Dewatering

Extraction

Conversion

Products

Conclusions

Chapter 9. Microalgal Cell Disruption and Lipid Extraction Techniques for Potential Biofuel Production

Introduction

Microalgal Lipid Composition and Distribution

Microalgal Lipid Extraction Mechanisms

Challenges in Microalgal Lipid Extraction Process

Limitations of Conventional Solvent-Based Extraction and Alternatives

Conclusion

Chapter 10. Conversion of Microalgae Biomass to Biofuels

Introduction to Microalgae-Based biofuel

Conversion of Microalgae Biomass into Biofuel

Conclusion

Chapter 11. Microalgal Biorefinery

Introduction

Microalgae to Biodiesel

Microalgae to Biogas

Microalgae to Biohydrogen

Microalgae to Bioethanol

Microalgae to Fertilizer

Microalgae to Animal Feed

Microalgae to Bioactive Compounds

Concluding Remarks

Chapter 12. Microalgal Biorefineries for Industrial Products

Introduction

Challenges of Algal Cultivation

Algal Biorefinery Concepts

Future Perspectives

Conclusions

Chapter 13. Biorefinery of Microalgae for Nonfuel Products

Introduction

Bioactive Compound from Microalgae

Diverse Use of Microalgae Biomass

Future Trends

Chapter 14. Recent Trends in Strain Improvement for Production of Biofuels From Microalgae

Introduction

Scope of Strain Improvement

Systems Biology: A Novel Paradigm

Synthetic Biology Approaches for Strain Improvement

Conclusions

Chapter 15. Microalgae to Biogas: Microbiological Communities Involved

Introduction

Microalgae to Biogas

Biochemical Process From the Sewage Microbiology Community

Interaction Mechanisms Between Microalgae—Bacteria in the Anaerobic Digestion Process

Molecular Techniques for the Anaerobic Sludge Microbiology Analysis—Contribution for Biogas Production

Case Study: Microbiological Communities Involved in Biogas Production From a Microalgae Culture

Concluding Remarks

Chapter 16. Microalgae-Based Biofuel Production Using Low-Cost Nanobiocatalysts

Introduction

Catalyst

Conclusion

Chapter 17. Biosynthesis of Nanomaterials Using Algae

Introduction

Green Synthesis of Nanomaterials

Nanoparticle Synthesis Using Algae

Factors Affecting the Synthesis Process

Application of Algae-Mediated Nanoparticles

Conclusion

Chapter 18. Life Cycle Assessment and Techno-Economic Analysis of Algal Biofuel Production

Introduction

LCA Methodology in Algal Biofuel Production

Results and Discussion for Existing LCA in Algal Biofuels

Results and Discussion of TEA for Algal Biofuels

Policies and Market Intensives for Algal Biofuel

Conclusions

Chapter 19. Environmental Resilience by Microalgae

Introduction

Availability of Nutrients in Wastewaters for Microalgae Growth

Treating Agro-Industrial and Industrial Wastewaters With Microalgae

Challenges in Treating Wastewaters With Microalgae

Challenges and Future Prospect of the End Use of Microalgae Cultivated on Wastewaters

Proof of Concept and Successful Cases

Chapter 20. Microalgae-based Remediation of Wastewaters

Introduction

Chapter 21. Resource Recovery From Waste Streams Using Microalgae: Opportunities and Threats

Introduction

Mechanism of Microalgae for Resource Recovery

Biochemicals Recovery from Waste Resources

Recent Developments and Opportunities for Resource Recovery

Index

Copyright

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Dedicated to

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List of Contributors

Iftikhar Ahmed,     Energy Research Centre, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan

M. Amirul Islam,     Laboratory for Quantum Semiconductors and Photon-Based BioNanotechnology, Department of Electrical and Computer Engineering, Faculty of Engineering, Université de Sherbrooke, Sherbrooke, QC, Canada

M. Anand,     Department of Chemistry, Science and Humanities Kingston Engineering College, Vellore, Tamil Nadu, India

Ambreen Aslam,     Department of Environmental Sciences, The University of Lahore, Lahore, Punjab, Pakistan

Muhammad Roil Bilad,     Chemical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia

Rolando Chamy,     Laboratorio de Biotecnología Ambiental, Escuela de Ingeniería Bioquímica, Facultad de Ingeniería, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile

Benjamas Cheirsilp,     Biotechnology for Bioresource Utilization Laboratory, Department of Industrial Biotechnology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla, Thailand

Min-Yee Choo,     Institute of Biological Sciences, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia

Olivia Córdova,     Laboratorio de Biotecnología Ambiental, Escuela de Ingeniería Bioquímica, Facultad de Ingeniería, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile

Tahir Fazal,     Biorefinery Engineering And Microfluidic (BEAM) Research Group, Department of Chemical Engineering, COMSATS University Islamabad, Lahore Campus, Lahore, Punjab, Pakistan

Che Ku Mohammad Faizal,     Faculty of Engineering Technology, Universiti Malaysia Pahang, Gambang, Pahang, Malaysia

M. Franco Morgado,     Instituto de Ingeniería, Universidad Nacional Autónoma de México (UNAM), Ciudad de México, México

D. García,     Center for Research in Aquatic Resources of Nicaragua, National Autonomous University of Nicaragua, Managua, Nicaragua

A. González-Sánchez,     Instituto de Ingeniería, Universidad Nacional Autónoma de México (UNAM), Ciudad de México, México

Mohd Dzul Hakim Wirzal,     Chemical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia

Pei Han,     School of Resources, Environmental & Chemical Engineering and Key Laboratory of Poyang Lake Environment and Resource Utilization, Ministry of Education, Nanchang University, Nanchang, Jiangxi, China

Javed Iqbal,     Department of Chemical Engineering, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan, Punjab, Pakistan

Kailin Jiao,     College of Energy, Xiamen University, Xiamen, Fujian, China

Keju Jing,     Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, The Key Lab for Synthetic Biotechnology of Xiamen City Xiamen University, Xiamen, Fujian, China

Joon Ching Juan,     Nanotechnology and Catalysis Research Center (NANOCAT), University of Malaya, Kuala Lumpur, Malaysia

Ahasanul Karim,     Faculty of Engineering Technology, Universiti Malaysia Pahang, Gambang, Pahang, Malaysia

Mohd Asyraf Kassim,     Bioprocess Technology Programme, School of Industrial Technology, Universiti Sains Malaysia (USM), Gelugor, Penang, Malaysia

Zaied Bin Khalid,     Faculty of Engineering Technology, Universiti Malaysia Pahang, Gambang, Pahang, Malaysia

Md Maksudur Rahman Khan,     Faculty of Chemical and Natural Resources Engineering, Universiti Malaysia Pahang, Gambang, Pahang, Malaysia

Michael Kornaros,     Laboratory of Biochemical Engineering and Environmental Technology (LBEET), Department of Chemical Engineering, University of Patras, Patras, Greece

Eleni Koutra,     Laboratory of Biochemical Engineering and Environmental Technology (LBEET), Department of Chemical Engineering, University of Patras, Patras, Greece

Shishir Kumar,     Nanomaterials and Bioprocessing Laboratory (NABLAB), Dan F. Smith Department of Chemical Engineering, Lamar University, Beaumont, TX, United States

Jia Jia Leam,     Chemical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia

Hwei Voon Lee,     Nanotechnology and Catalysis Research Center (NANOCAT), University of Malaya, Kuala Lumpur, Malaysia

Jingjing Li,     School of Resources, Environmental & Chemical Engineering and Key Laboratory of Poyang Lake Environment and Resource Utilization, Ministry of Education, Nanchang University, Nanchang, Jiangxi, China

Tau Chuan Ling,     Institute of Biological Sciences, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia

Lu Lin,     College of Energy, Xiamen University, Xiamen, Fujian, People of Republic of China

Qian Lu,     School of Resources, Environmental & Chemical Engineering and Key Laboratory of Poyang Lake Environment and Resource Utilization, Ministry of Education, Nanchang University, Nanchang, Jiangxi, China

Yinghua Lu,     Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, The Key Lab for Synthetic Biotechnology of Xiamen City, Xiamen University, Xiamen, Fujian, China

Yohanis Irenius Mandik,     Department of Chemistry, Faculty of Mathematics and Natural Sciences, University of Cenderawasih, Jayapura, Indonesia

Emmanuel Manirafasha,     Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, The Key Lab for Synthetic Biotechnology of Xiamen City, Xiamen University, Xiamen, Fujian, China

H.O. Méndez-Acosta,     Centro Universitario de Ciencias Exactas e Ingenierías, Universidad de Guadalajara, Guadalajara-Jalisco, México

Sandhya Mishra,     Academy of Scientific & Innovative Research (AcSIR), CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat, India

Dongyan Mu,     School of Environmental and Sustainability Sciences, Kean University, Union, NJ, United States

Theophile Murwanashyaka,     Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, The Key Lab for Synthetic Biotechnology of Xiamen City, Xiamen University, Xiamen, Fujian, China

Tabish Nawaz

Environmental Science and Engineering Department (CESE), Indian Institute of Technology Bombay, Mumbai, Maharashtra, India

Center for Advances in Water and Air Quality, Lamar University, Beaumont, TX, United States

Theoneste Ndikubwimana,     Kibogora Polytechnic, Rusizi, Rwanda

Eng-Poh Ng,     School of Chemical Sciences, Universiti Sains Malaysia, Penang, Malaysia

Lee Eng Oi,     Nanotechnology and Catalysis Research Center (NANOCAT), University of Malaya, Kuala Lumpur, Malaysia

Imran Pancha,     Academy of Scientific & Innovative Research (AcSIR), CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat, India

Ashok Pandey,     Distinguished Scientist, CSIR-Indian Institute for Toxicology Research, Lucknow, Uttar Pradesh, India

Won-Kun Park,     Department of Chemistry & Energy Engineering, Sangmyung University, Seoul, Republic of Korea

Antonino Pollio,     Department of Biology, University of Naples Federico II, University Complex of Monte Sant’Angelo, Naples, Italy

Ashiqur Rahman,     Nanomaterials and Bioprocessing Laboratory (NABLAB), Dan F. Smith Department of Chemical Engineering, Lamar University, Beaumont, TX, United States

Shristi Ram,     Academy of Scientific & Innovative Research (AcSIR), CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat, India

J. Ranjitha,     CO2 Research and Green Technologies Centre, Vellore Institute of Technology, Vellore, Tamil Nadu, India

Naim Rashid,     Department of Chemical Engineering, COMSATS University Islamabad, Lahore, Punjab, Pakistan

Fahad Rehman,     Biorefinery Engineering and Microfluidic (BEAM) Research Group, Department of Chemical Engineering, COMSATS University Islamabad, Lahore Campus, Lahore, Punjab, Pakistan

Dianbandhu Sahoo,     Institute of Bioresources and Sustainable Development, A National Institute under Department of Biotechnology, Govt. of India, Takyelpat, Imphal, Manipur, India

Muhammad Saif Ur Rehman,     Department of Chemical Engineering, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan, Pakistan

Myrsini Sakarika,     Center for Microbial Ecology and Technology (CMET), Ghent University, Gent, Belgium

Thinesh Selvaratnam,     Department of Civil and Environmental Engineering, Lamar University, Beaumont, TX, United States

M.L. Serejo,     Centro Universitario de Ciencias Exactas e Ingenierías, Universidad de Guadalajara, Guadalajara-Jalisco, México

Ali Shan,     Department of Environmental Sciences, The University of Lahore, Lahore, Punjab, Pakistan

Sirasit Srinuanpan,     Biotechnology for Bioresource Utilization Laboratory, Department of Industrial Biotechnology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla, Thailand

Jean-Philippe Steyer,     Laboratory of Environmental Biotechnology, National Institute of Agronomic Research, University of Montpellier, Narbonne, France

Yong Sun,     College of Energy, Xiamen University, Xiamen, Fujian, China

Tan Kean Meng,     Bioprocess Technology Programme, School of Industrial Technology, Universiti Sains Malaysia (USM), Gelugor, Penang, Malaysia

Xing Tang

University of Rwanda-College of Education, Kigali, Rwanda

Fujian Engineering and Research Center of Clean and High-Valued Technologies for Biomass, Xiamen Key Laboratory of Clean and High-Valued Utilization for Biomass, Xiamen University, Xiamen, Fujian, China

Antonia Terpou,     Laboratory of Biochemical Engineering and Environmental Technology (LBEET), Department of Chemical Engineering, University of Patras, Patras, Greece

A. Toledo-Cervantes,     Centro Universitario de Ciencias Exactas e Ingenierías, Universidad de Guadalajara, Guadalajara-Jalisco, México

Panagiota Tsafrakidou,     Laboratory of Biochemical Engineering and Environmental Technology (LBEET), Department of Chemical Engineering, University of Patras, Patras, Greece

Sabeela Beevi Ummalyma,     Institute of Bioresources and Sustainable Development, A National Institute under Department of Biotechnology, Govt. of India, Sikkim Centre, Tadong, Gangtok, Sikkim, India

S.V. Vamsi Bharadwaj,     Academy of Scientific & Innovative Research (AcSIR), CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat, India

S. Vijayalakshmi,     CO2 Research and Green Technologies Centre, Vellore Institute of Technology, Vellore, Tamil Nadu, India

Yusuf Wibisono,     Bioprocess Engineering Department, Universitas Brawijaya, Malang, Indonesia

Chunhua Xin,     School of Management, China University of Mining and Technology (Beijing Campus), Beijing, China

Yuanchao Xu,     College of Biologic Engineering, Qi Lu University of Technology, Jinan, Shandong, China

Abu Yousuf,     Department of Chemical Engineering & Polymer Science, Shahjalal University of Science and Technology, Sylhet, Bangladesh

Qamar uz Zaman,     Department of Environmental Sciences, The University of Lahore, Lahore, Punjab, Pakistan

Xianhai Zeng,     College of Energy, Xiamen University, Xiamen, Fujian, China

Wenguang Zhou,     School of Resources, Environmental & Chemical Engineering and Key Laboratory of Poyang Lake Environment and Resource Utilization, Ministry of Education, Nanchang University, Nanchang, Jiangxi, China

Gaetano Zuccaro,     Laboratory of Environmental Biotechnology, National Institute of Agronomic Research, University of Montpellier, Narbonne, France

About the Editor

Abu Yousuf holds a PhD in Chemical Engineering from the University of Naples Federico II, Italy. His primary research interests include biorefinery, bioenergy, bioremediation, and waste-to-energy. He has published more than 50 papers in reputed ISI and Scopus indexed journals and 5 book chapters. He has been editing 3 books, will be published by Elsevier, and has been serving as an editorial board member of several reputed journals. He won the UNESCO Prize on E-learning course of Energy for sustainable development in Asia, Jakarta, Indonesia, 2011. He attended the BIOVISION.Next Fellowship Programme 2013 at Lyon, France, after a selection based on scientific excellence, mobility, and involvement in civil society. He also received several awards for his research outcomes from UK, Malaysia and Bangladesh. He successfully accomplished 10 research project including the grants provided by The World Academy of Science (TWAS), Italy; Ministry of Higher Education, Malaysia; and Ministry of Science and Technology, Bangladesh. Dr. Yousuf is a member of IChemE, American Chemical Society (ACS), American Association for Science and Technology (AASCIT), and Bangladesh Chemical Society (BCS). He has 12 years' experience in teaching at the undergraduate and postgraduate levels, having very good remarks from the students. Currently, Dr. Yousuf is serving as a Professor in Chemical Engineering and Polymer Science, Shahjalal University of Science and Technology, Bangladesh. Previously he held the position of Senior Lecturer at Faculty of Engineering Technology, Universiti Malaysia Pahang, Malaysia. He has presented his research work in Germany, France, Italy, India, Vietnam, Malaysia and Bangladesh. He can be contacted at [e-mail]/[e-mail].

Preface

Bio-based industries are drawing attention because of their major role in energy security and climate change mitigation during the 21st century. At the same time, microalgae have come into sight as a potential nonedible feedstock with advantages over traditional land crops, such as high productivity, continuous harvesting throughout the year, and minimal problems regarding land use and race with food. Therefore, understanding of microalgae biorefinery is a significant part of the growing demand for energy, fuels, chemicals, and materials worldwide.

In this context, the book is intended to compile significant technological challenges to produce economically competitive algae-derived biofuel, such as efficient methods for cultivation; improvement of harvesting and lipid extraction techniques; optimization of conversion/production processes of fuels and co-products; integration of microalgae biorefineries to several industries; environmental resilience by microalgae; and techno-economic and life cycle analysis of production chain to get the maximum benefits from microalgae biorefineries.

The book starts (Chapter 1) with basic information of microalgae, like biology of microalgae, their lipid content, mass cultivation systems with their comparison, and influential growth factors. Chapters 2–7 address mainly microalgae cultivation, harvesting, nutrients metabolism, and bioreactor design. They also discuss the modification of microalgae cultivation via engineering approaches such as photobioreactor development and mode of cultivation to improve microalgae biomass production.

Chapters 8–10 describe the current technologies published in recent studies on downstream processes of microalgal biomass into bioproducts including biodiesel, biogas, hydrogen, pigments, and fatty acids as end products. These chapters further explain how to cut down the cost of microalgae in downstream processes particularly in the stages of harvesting and dewatering, extraction, fractionation, and conversion.

Chapters 11–13 address the challenges of microalgal cultivation and exploitation of different algal metabolites for various industrial products (fuel and nonfuel) in the biorefinery concept to solve the issues associated with microalgal biomass and its future perspectives. In this regard, the chapters highlight fuel-based products such as biodiesel, biogas, biohydrogen, and bioethanol, and nonfuel products such as fertilizer, forage, food, feed, and bioactive compounds. These chapters also provide a perspective to improve their yield, and outline a strategy to integrate biorefinery with current environmental techniques.

Chapter 14 introduces contemporary genetic engineering techniques and tools to improve biofuel and biochemical production in various microalgae. They also discuss various system biology tools like genomics, transcriptomics, etc., to improve the final product yield using various microalgae.

Chapter 15 presents microbiological communities associated with anaerobic sludge for the biomethanization of a microalgal biomass that should be considered for the optimal development of anaerobic digestion to produce biogas.

Chapter 16 describes the various types of nano-biocatalysts used for microalgae-based biodiesel production using transesterification process and their merits in the current industrial application.

Chapter 17 focuses on a green chemistry-based approach on the biosynthesis of nanomaterials using algae. Special attention is placed on AgNP synthesis and microwave-assisted synthesis methods. Various factors that affect nanomaterial synthesis such as pH, temperature, incubation time, ionic strength, light intensity, and algal biomass have been extensively discussed.

Chapter 18 provides a critical review of the existing methodology and application of life cycle assessment (LCA) and techno-economic assessment (TEA) on algae cultivation and algal biofuel production.

Chapters 19–21 emphasize on the direct benefits of environmental bioremediation through microalgae culture. These chapters provide the viability of environmental resilience of some microalgae strains for treating highly polluted wastewaters. The chapters also show the pathway how to achieve major breakthrough by qualifying microalgae as a sustainable biorefinery feedstock and by resource recovery from waste streams through their culture.

Researchers and academicians with strong scientific knowledge and practical experiences have shared their thoughts in this book. We trust the book will enrich the foresight of current and future researchers who are dedicatedly working on microalgae-based products.

Abu Yousuf

Sylhet, Bangladesh

Acknowledgment

We are expressing our gratitude to all distinguished authors for their thoughtful contribution to make this book project a success. Their patience and diligence in revising the first draft of the chapters after assimilating the suggestions and comments of reviewers are highly appreciated.

We would like to acknowledge the solicitous contributions of all the reviewers who spent their valuable time in a constructive and professional manner to improve the quality of the book.

We are grateful to the staff at Elsevier, particularly Ms. Raquel Zanol (Acquisitions Editor), who supported us tremendously throughout the project and for her great and encouraging mind. We also acknowledge Dr. Peter W. Adamson (Editorial Project Manager), Poulouse Joseph (Senior Project Manager) and Swapna Praveen (Copyrights Coordinator) for their cordial handling of the book.

Chapter 1

Fundamentals of Microalgae Cultivation

Abu Yousuf

Abstract

Microalgae have gained attention in the past few decades due to their potential applications in many areas such as food supplements, lipids, enzymes, biomass, polymers, toxins, pigments, wastewater treatment, animal feed, and green energy. To culture microalgae in industrial scale and make them commercially viable, it is essential to study in depth their characteristics, cultivation system, and factors affecting the cultivation. Microbial lipid is the most attractive component of microalgae to produce biofuels. Competence of lipid production by microalgae is highly dependent on the cost of reactor design, wide range of nutritional substrates, scalability, parasitic energy demand, metabolic function, etc. Therefore, this chapter describes the fundamental issues of microalgae and their cultivation.

Keywords

Cultivation system; Growth factors; Microalgae; Microbial lipid

Introduction

Microalgae or microphytes are microscopic eukaryotic organisms, usually found in freshwater and marine systems, use solar energy to produce ATP, which is converted to lipid, carbohydrate, and proteins by its metabolic function. Microalgae offer great promise in contributing to renewable bioenergy, as they have high lipid content, rapid growth rate, and aquatic growth environment using solar energy and also avoid the food versus fuel debate. Although microalgae have a wide range of applications such as food supplements, lipids, enzymes, biomass, polymers, toxins, pigments, tertiary wastewater treatment, and green energy, in the past few decades, it has been considered as highly potential source of biofuels.

Algae are having both plant-like and animal-like characteristics. Plant-like algae are typically found in aquatic environments that contain chloroplasts and are capable of photosynthesis. Unlike higher plants, algae lack vascular tissue and do not possess roots, stems, leaves, or flowers. Animal-like algae are having of flagella and centrioles and are capable of feeding on organic material in their metabolism. The size of algae varies from single cell to giant multicellular species, and they can survive or grow in multivariate environments such as in fresh water, salt water, or wet soil or on moist rocks. They can be reproduced by sexually or asexually or by a combination of both processes through alternation of generations.

Algae have been used in the past as a way to recycle some of the nutrients from wastewater sources and also as a step in industrial wastewater treatment. As long as the world's population continues to grow, the source of wastewater only gets greater and greater. Utilizing this harmful product as a nutrient source, microalgae are capable of producing lipid that is considered as a potential source of biodiesel. However, three aspects of microalgae production that will strongly influence the future sustainability of algal biofuel production are the energy and carbon balance, environmental impacts, and production cost.

To consider microalgae as a viable feedstock, overall energy and carbon balance must be favorable. Comparing biomass production system in terms of net energy ratio (NER), a positive energy balance should be required. When NER is defined as the sum of the energy used for cultivation, harvesting, and drying, divided by the energy content of the dry biomass, then, if it is less than unity, the process produces more energy than it consumes. In realistic case, most systems have the NER value   >   1. In the systems that have NER<1, if drying, dewatering processes, and lipid extraction are considered, the NER changes from 0.05–0.1 to 0.5–0.75 [1].

Recovery and preparation of microalgal biomass for transesterification reaction requires more than 20%–30% of the total cost of biofuel preparation. Floatation, centrifugation, coagulation-flocculation, and filtration are some of the mostly used ways for separation; however, no single best method for harvesting is not yet involved. Most methods used to extract the oil from algal biomass rely on a dry biomass product. Lyophilization, oven drying, or forced air drying also causes an additional cost. For these reasons, commercial-grade algal oil production is still not cost-effective. However, microalgae are given priority over other energy crops because of the following:

• They can be cultivated in nonarable land.

• They can be grown on ponds and photobioreactors.

• They can tolerate wide range of pH, salinity, and temperature.

• They are continually cultivable, not seasonally harvested.

• They can mitigate CO2 from industrial and atmospheric sources.

• Complete usage of biomass (proteins, lipids, and carbohydrates).

• They are not finite resource, i.e., renewable and sustainable.

Therefore, the aim of the chapter is to address the basic issues of microalgae cultivation, which should be considered to make them sustainable for microalgae-based industries.

Fundamental Characteristics of Algae

Algae are broadly classified into two categories: macroalgae and microalgae. Up to June 2012, from 30,000 to more than 1 million species have been estimated, of which 44,000 names have probably been published, and 33,248 names have been processed [2].

Biology of Microalgae

Microalgae is a general term for the algae that form a multicellular thallium at least in one stage of the life cycle. It can also show differentiation between tissues and reproductive system than unicellular microalgae. The largest multicellular algae are called seaweed, which can be well over 25   m in length. The oil content of macroalgae usually ranges between 10% and 30%.

Microalgae are simple microscopic heterotrophic or autotrophic photosynthetic organisms, also called phytoplanktons by biologists ranging between 1 and 50   μm in diameters. These are usually found in pond/damp places or aquatic environment. Most species contain chlorophyll, which uses photonic energy (light), carbon dioxide (CO2) and water to synthesize carbohydrates (energy storage) and make biomass (algae growth).

In a batch culture system, algal growth experiences five different phases. In this system, inoculum with a fixed volume of nutrient media is charged into the system. As the microalgae replicate, the nutrients depleted and final product obtained. The phases are as follows. (1) Lag phase: Initial period of slow growth where microalgae take time for adaptation into the new environment. The length of the lag phase depends on the size of the inoculum as well as shock of the environment. (2) Exponential: Rapid growth and often cell division occurs when there is an appreciable amount of cell and microalgae grow very rapidly. (3) Declining relative growth: This phase occurs when a growth requirement for cell division is limiting. (4) Stationary: Cell division slows due to the lack of resources necessary for growth. (5) Death/lysis: Cells begin to die due to lack of nutrients [3,4] (Fig. 1.1).

Microalgae are easy to cultivate and can tolerate broad range of pH, salinity, and temperature. They commonly double every 24   h. During the peak growth phase, some microalgae can double every 3.5   h. Oil contents of microalgae are usually between 20% and 50% (dry weight), while some strains can reach as high as 80%. It has the ability to survive much more extreme condition, which triggers this to generate higher lipid content [5].

Fig. 1.1 Schematic growth curve of a microalgal batch culture system.

Lipid Content of Microalgae

Although several kinds of microorganisms may accumulate oils, such as microalgae, bacillus, fungi, and yeast, not all of them are suitable for biodiesel production (Table 1.1). Microalgae offer high lipid contents, but they need a larger acreage to be cultured and longer fermentation periods than bacteria. Although bacteria accumulate lower lipid than microalgae, they offer higher growth rates (only 12–24   h is needed for the maximum biomass concentration to be reached) and easy culture methods. Besides this, the most efficient oleaginous yeasts Cryptococcus curvatus can accumulate storage lipids up to >60% on a dry weight basis. In addition, when the C. curvatus grow under N-limiting conditions, these lipids usually consist of single oil cell (SOC) 90% w/w triacylglycerol with a percentage of saturated fatty acids (% SFAs) of about 44%, which is similar to many plant seed oils [6].

Algae Mass Cultivation System

At present, approximately 5000   tons of dry algae are produced per year worldwide. It is considered as green gold for future [4]. Several cultivation techniques are currently employed for the large-scale production of microalgae biomass; microalgae can be normally cultivated in the open-culture systems (lakes or ponds) due to cheap and easy process and also in the closed-culture systems called photobioreactors (PBRs) due to higher yield of biomass and better control opportunity. Recently, many researchers try to combine these two to obtain the best case [5].

Photobioreactor

A PBR is a closed (or mostly closed) vessel for phototrophic production where energy is supplied via electric lights [8]. PBRs can be located indoors or outdoors depending upon the light collection and distribution systems and their commercial feasibility. In PBRs, the culture medium is enclosed in a transparent array of tubes or plates, and the microalgal broth is circulated from a central reservoir [9]. PBR can be different kind (Table 1.2), like polyethylene bags, glass fibers cylinder, flat modular photobioreactor, tubular inclined, segmented glass plate, and annular photobioreactor. The main objective of any PBR is the reduction of biomass production costs. To achieve the goal, numerous studies have been done on catalysts improvement, shaping of the PBR, controlling environmental parameters during cultivation, and aseptic designs. The controlling of operational parameters such as pH, temperature, and gas diffusion is also a vital issue in PBR [10].

Table 1.1

Open Pond

Open pond cultivation system typically consists of simple water tank or bigger earthen-bank ponds where nutrients are added from outsource. Natural light plays a role in photosynthesis, and CO2 comes from atmosphere. The pond is usually designed in a raceway or track configuration, in which a paddlewheel provides circulation and mixing of the algal cells and nutrients. The raceways are typically made from poured concrete, or they are simply dug into the earth and lined with a plastic liner to prevent the ground from soaking up the liquid. Baffles in the channel guide the flow around bends that also minimize space and loss. Medium is added in front of the paddlewheel, and algal broth is harvested behind the paddlewheel, after it has circulated through the loop. A comparison between open pond and closed-system PBR is summarized in Table 1.3.

Heterotrophic and Autotrophic Microalgal Culture System

Algae that require light source as energy to run photosynthesis are called autotrophic. Some species of algae are heterotrophic, meaning that they use organic carbon substrates such as glucose or acetate for energy and do not require sunlight to grow. There are some kinds of algae that can operate in both an autotrophic and heterotrophic manner depending on the available resources. These algae species are referred to as mixotrophic [13].

Heterotrophic and mixotrophic algae are very interesting to some researchers, as they grow 24   h a day compared with the autotrophic algae that grow 12   h a day. Heterotrophic algae are independent of light source, which makes their growth condition energy intensive and their surface to volume ratio lower than PBRs and open pond.

This makes growing heterotrophic algae easier to scale up. The growth systems are relatively simple and cheap to set up and can provide high yields of algae per volume. However, the systems require a source of organic carbon, unlike autotrophic systems. Some researchers suggest that heterotrophic growth systems may be better for producing high biomass and high lipid contents.

Algae Growth Factor

Major key components for algal growth are a growth medium with proper nutrients, a light source for photosynthesis, and CO2 or air flow. All of these growth factors must be specified for successful microalgae cultivation for a specific purpose, which can vary from species to species [14]. These factors can be divided into three categories (Table 1.4):

Table 1.2

Environmental Factors

pH

pH measures the level of acidity or alkalinity that a body of water has. Most algae have pH optima for growth generally 6–8 and photosynthesis ability in the neutral to alkaline pH range. Variation of pH affects the growth in a number of ways. pH increases during daytime caused by photosynthetic CO2 assimilation by the algae followed by decrease in pH at night due to the respiratory process of the community [8]. There is a relationship between CO2 concentration and pH of microalgal culture medium. It is related to the chemical equilibrium among chemical species such as CO2, H2CO3, HCO3 − , and CO3 ²− . The equilibrium of these species is pH dependent when CO2 is predominant at pH below 7.0 and CO3 ²− predominant above pH 10. Microalgae have been shown to cause a rise in pH to 10–11 because of CO2 uptake photosynthetically to convert its biomass [15]. Increasing CO2 can lead to higher biomass accumulation but leads to lower the pH value, which has adverse effect on microalgal physiology. However, when pH increases too high, photosynthesis can be limited due to scarcity of CO2

Table 1.3

Nutrients

To grow algae, macronutrients should contain nitrogen and phosphorus mainly (silicon is also required for saltwater algae). In addition, trace metals, such as Fe, Mg, Mn, B, Mo, K, Co, and Zn, are also needed. CO2 fixation is also necessary to build up a balanced medium for optimum growth. Microalgae biomass usually consists of around 40%–50% carbon, 4%–8% nitrogen, and 0.1% phosphate by dry weight. In nature, some of these can be found easily from mineral source, and some can be found by bacterial metabolism. Nitrogen is abundant in nature because it fixes by bacteria continuously, while phosphorus is limited, which is effectively bound as orthophosphate in sediment. Nutrient levels, especially nitrogen and phosphorus combinedly, are very important in the production of lipids. Many articles have shown that a nitrogen-deficient growth medium triggers the algae to produce higher levels of lipids. Under phosphorus limitation, Xin et al. [16] reported lipid content of 53% for Scenedesmus sp. With the same species, nitrogen limitation only induced a lipid content of 30%. Nutrient deficiencies and excess nutrients, both, can cause physiological and morphological changes in microalgae, since they can inhibit some of the vital metabolic pathways. Recently, researchers are focused upon two-phase growth system, where in the first phase, algae are grown in nutrient-abundant medium and then transferred to a nutrient-deficient medium where lipid accumulation is boosted up [17].

Table 1.4

Temperature

Most algae of interest for lipid production have a temperature tolerance between 15 and 40°C. Researchers [15] have shown that many of the oil-producing algae species grow best between 25 and 30°C. The optimal growth temperature varies by species and the desired algae response. But controlling the temperature at outdoor condition is tough and expensive. Not only the extreme temperature but also the evaporation of media, overheating and cooling at outdoor condition, and lipid composition are also major issues for algal growth. Chaisutyakorn et al. [18] found that higher temperature is responsible for saturated lipid accumulation and lower temperature for unsaturated lipid accumulation. Contrarily, many researchers [19,20] found there is no effect of temperature upon lipid accumulation. So, there exist contradictory views about this issue.

Processing Parameters

Mixing

Mixing is important to prevent sedimentation of algae and to move the algae between the light and dark regions of the pond/reactor. Without any forced mixing, algae at the surface absorb all the available light and can become photoinhibited, while algae deeper in the media are light deprived. It also helps to maintain a homogeneous cell concentration in medium. Mixing can be provided in several ways such as open ponds use a mechanical stirrer (a paddlewheel in raceways) and bubbling in gas (air, CO2) to provide mixing. PBRs use pumps and bubbling in gas for mixing [8]. It is also noted that many microalgae species cannot tolerate vigorous mixing.

Light intensity

When algae are cultivated photosynthetically, the efficiency of photosynthesis is a crucial determinant in their productivity since it affects the growth rate, biomass production, and lipid accumulation. Effect of light intensity depends on depth of the culture medium and density of the algal biomass. If the depth and cell concentration of the culture is higher, light intensity must be increased to penetrate through the medium. On the other hand, direct sunlight or high-density artificial light may act as photoinhibitor. Overheating caused by both natural and artificial illumination is also unexpected and should be avoided. It is suggested that light intensity of 1000 lux is suitable for the culture in Erlenmeyer flasks; 5000–10,000 is required for larger volumes. A light/dark system is required for the efficient photosynthesis of microalgae because light is needed for photochemical phase to produce ATP and NADPH and dark for biochemical phase to synthesize essential biomolecules for microbial growth.

Biotic Factors

Predators

Invasive species and predators can be any kind of living organism that is totally unexpected in the microalgae culture area because they inhibit microalgae growth, pollute the culture medium, and deficit the nutrient. Predators may be fungus, bacteria, insect, and even unwanted microalgae species. To avoid any potential issues from invasive and predator species, industrial algae growth is mostly limited to extremophile algae species, which can grow in extreme environments in which competing species are unable to survive. Open ponds are susceptible to invasion by low oil–producing algae strains, while PBRs prevent this by keeping the algae contained from the outside environment.

Traditional Sources of Biodiesel and Their Limitations

To deal with deteriorated situation of the whole world energy supply, energy environment, and energy security, renewable biofuels are receiving considerable attention as substitute [21]. One of the most prominent renewable energy resources is biodiesel, which is produced from renewable biomass by transesterification of triacylglycerols, yielding monoalkyl esters of long-chain fatty acids with short-chain alcohols, for example, fatty acid methyl esters and fatty acid ethyl esters. Traditionally, biodiesel is obtained from vegetable oils such as soybean oil [22,23], jatropha oil [24], rapeseed oil, palm oil, sunflower oil, corn oil, peanut oil, canola oil, and cottonseed oil [25]. Apart from vegetable oils, biodiesel can also be produced from other sources such as animal fat (beef tallow, lard), waste cooking oil, greases (trap grease, float grease), and algae. In South East Asia, Europe, the United States, and China, palm oil, rapeseed oil, transgenic soybeans, and wasting oil, respectively, were used to produce biodiesel. However, all these plant oil materials require energy and acreage for sufficient production of oilseed crops. Likewise, animal fat oils need to feed these animals. In spite of the favorable impacts that its commercialization could provide, the economic aspect of biodiesel production has been restricted by the cost of oil raw materials. If plant oil was used for biodiesel production, the cost of source has accounted to 70%–85% of the whole production cost [26]. Therefore, taking into account of these inhibition factors, exploring ways to reduce the high cost of biodiesel is of much interest in recent research, especially for those methods concentrating on lowering the cost of oil raw material. Microorganisms (microalgae, yeast) have often been considered for the production of oils and fats as an alternative to agricultural and animal sources. Synthesis of microbial lipids or single cell oil have some unique advantages over vegetable oils, such as they can be cultivated on degraded and nonagricultural lands that avoid use of high-value lands and crop-producing areas and can utilize salt and wastewater streams, thereby greatly reducing freshwater use [27]. Apart from these conditions, a comparison between first-, second-, and third-generation biodiesels is presented in Table 1.5.

Microalgae as an Alternative

The composition of the biomass is useful for characterizing the best use of microalgae species. The biomass of microalgae contains a number of compounds such as proteins and lipids, which make up the organelles. Algal biomass contains three main components: carbohydrates, proteins, and lipids/natural oil. For example, with the knowledge that biodiesel is made from oils, a microalga with a very high protein content and low lipid content would not be useful as a biofuel feedstock (Table 1.6). It is found that the bulk of the natural oil made by microalgae is in the form of triacylglycerides (TAGs), which is the right kind of oil for producing biodiesel. The fatty acids attached to the TAG within the algal cells can be both short- and long-chain hydrocarbons. The shorter chain length acids are ideal for the creation of biodiesel, and some of the longer ones can have other beneficial uses. Some microalgae species with high lipid content are listed in Table 1.6.

Table 1.5

Table 1.6

Conclusion and Recommendation

Microalgae provide us oxygen we need to breathe by photosynthesis. For this reason, we owe them our lives, but they will also improve our lifestyle. Since they are rich in proteins, carbohydrates, and lipids, which are the source of many beneficial products for mankind, such as human nutrition, feed, agriculture, aquaculture, cosmetics, medicinal, and others, the scientific community agrees that, in the near future, microalgae will competitively generate clean energy and third-generation biofuels, contributing therefore to a sustainable development in both environmental and circular economy. Furthermore, recent research and interest upon bioenergy sector has renewed again; it may also be found that algal biofuels will play a vital role in future, and attention should be given on the following:

• Optimization of the culture parameters necessary for high yields of biomass and total lipid content

• Significant reductions in complexity of cultivation and costs

• Adoption of dual-benefits large-scale industrial processes, such as wastewater treatment and biofuels production

• Development of the mathematical modeling-based process, before industrial trial and scale-up.

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Chapter 2

Microalgae Cultivation Systems

Gaetano Zuccaro, Abu Yousuf, Antonino Pollio, and Jean-Philippe Steyer

Abstract

The potential of microalgae as an alternative energy source has received much attention in recent years. Microalgae offer interesting features to qualify them as alternative feedstocks for several biorefinery applications. However, the general requirements for successful microalgal cultivation include growth factors such as temperature, light, nutrients, pH, and the different systems. This chapter reviews these aspects and includes discussion regarding the main parameters that could affect their growth and the future applications. Technology integration is still inevitable to off-set the cost of microalgae biomass processing.

Keywords

Cultivation system; Growth mode; Microalgae; Nutrient supply; pH; Temperature

Introduction

Microalgae are prokaryotic and eukaryotic cellular organisms with a size from a few μm to ca. 200   μm, able to produce around 50% of all O2 on Earth via photosynthesis   10⁴ are described in literature [2] and classified as Chlorophyceae (green algae), Cyanophyceae (blue-green algae), Chrysophyceae (golden algae), Rhodophyceae (red algae), Phaeophyceae (brown algae), and Bacillariophyceae (diatoms).

The potential of microalgae has attracted increasing interest in research and industrial fields because of their extensive applications such as renewable energies, pharmaceuticals, and nutraceuticals. Indeed, they are different in some aspects because it is possible to cultivate them in the vicinity of already existing industrial sites as they do not depend on the availability of fertile lands like in the case of bioprocesses that use feedstocks, like lignocellulosic biomasses, and need the transport to the biorefinery plants. This factor represents a way to facilitate the pretreatment processes and to reduce the overall production costs and the environmental concerns.

Microalgae cultivation requires specific environmental conditions including temperature ranges, light intensities, mixing conditions, nutrient composition, and gas exchange. They can be cultured using different metabolic pathways (photoautotrophic, heterotrophic, and mixotrophic) and by using different cultivations systems, commonly classified as open and closed systems. This chapter will provide an overview of the fundamentals to determine the future role of microalgae in biorefinery applications.

Growth Factor Affecting Microalgal Cultures

The growth of microalgae is affected by not only several factors such as temperature, light, nutrient availability, gas exchange, salinity, cell density, pH but also operational parameters such as fluid and hydrodynamic stress, mixing, culture depth, dilution rate, and harvest frequency [3].

Temperature

Physiological and morphological responses of microalgal growth, including photosynthesis and carbon fixation, are strictly related to the temperature C) (Table 2.1).

C C, due to chlorophyll instability.

The importance of the optimal temperature range is also related to the carbon fixation. Indeed, higher temperatures enhance CO2 absorption and fixation but represent an inhibitor factor for the respiration metabolism and for the photosynthetic proteins as they disturb the energy balance in cells. High temperatures also reduce cell size and microbial biomass growth (due to the affinity of ribulose for CO2), particularly in outdoor culture systems.

The effect of moderately elevated temperatures has also been found in the activation state of ribulose-1,5-bisphosphate (Rubisco), an enzyme able to act as an oxygenase or as carboxylase, depending on the relative amount of O2 and CO2 present in the chloroplast. The CO2 fixation activity of Rubisco enzyme is affected by the rising temperature up to a certain level and then declines [24]. Temperature can also be used as a stress treatment to induce the production of valuable metabolites. Because the temperature has an evident impact on the photosynthesis, it is difficult to evaluate the kinetic equation able to describe this phenomenon.

Table 2.1

Bechet et al. [25] studied different approaches, that can be summarized as uncoupled and coupled, where μ (h −¹), specific growth rate of photosynthesis is the product of two distinct functions of light intensity (Monod function) and temperature (Arrhenius equation) [Eq. 2.1]:

(2.1)

where μ is the specific growth rate (h −¹), μ m,0 is the maximum specific growth rate (h −¹), E a is the activation energy for photosynthesis (J), k is the Boltzmann constant (J K −¹), T is the temperature (K), I av is the average light intensity in the culture broth (μmol m −²s −¹), and K is a light constant (μmol m −²s −¹).

The potential interdependence of light and temperature is defined according to Eq. (2.2):

(2.2)

where μ m (T) is the maximum specific growth rate (h −¹) at the temperature T (°C), β I is a constant, I is the light intensity (μmol/m²s), and I opt (T) is the optimum light intensity for photosynthesis (μmol m −²s −¹) at the temperature T (°C).

Light

There is a direct relationship between microalgae growth, light intensity, and cultivation duration because the variation of the latter ones is able to directly affect photosynthesis and the related biochemical composition as well as biomass yield [26].

There is a relationship between light intensity (I) and rate of photosynthesis (P) as shown in Fig. 2.1 [25], where is possible to observe three different light regimes:

1. I<Ik (the rate of photosynthesis is proportional to low light intensities and the photosynthesis is limited by the rate of photon capture);

2. Ik(the rate of photosynthesis is usually maximal and independent from light intensity. This regime is light saturated, it means that the rate of photosynthesis is limited by rate of reactions following the photon capture); and

3. I>Iinhib (the rate of photosynthesis starts to decrease with the light intensity which, above a certain level can damage light receptors, such as key proteins, in the chloroplasts. This regime is known as photoinhibition).

The optimum level of light intensities for most of microalgae species are about 200–400   μmol   m −²   s −¹ [27], and for some microalgal species, it could also be equal to 100   μmol   m ² s −¹.

Light penetrates through the cell medium, but it is also attenuated according to Lambert–Beer's law [Eq. 2.3].

(2.3)

where I(l) is the local light intensity at a distance l from the external surface; I 0 , the incident light intensity; σ, the extinction coefficient and X, the cell concentration.

Light reactions provide the conversion of light energy in chemical energy in the form of short-term energy storing molecules. This is possible because chlorophyll molecules absorb photons, which induce the excitation of a pair of electrons, leading indirectly to ATP and NADPH production. However, when the light intensity surpasses a limit, it can represent the cause of the photoinhibition and photooxidation, which negatively influences cell density growth [28]. Moreover, the phenomenon of photoinhibition is also related to the preexposure to high or low irradiances. Indeed, Beardall and Morris [29] demonstrated a dynamic effect known as hysteresis, where a lower productivity of algae cells preexposed to high light intensity was observed if compared to productivity of cells preexposed to a dark regime, that can be caused to overestimate productivity, for example, during outdoor cultivation.

On the other hand, optimal light intensity needs to be experimentally evaluated in each case to maximize CO2 assimilation with a minimum rate of photorespiration and as little photoinhibition as possible [25]. The photoinhibition is associated to self or mutual shading effects, in which cells close to the bottom are shaded from the cells on the surface. One of the solutions identified to solve this problem is, for example, using of LED lights instead of fluorescent tubes that are commonly used [30].

Microalgal photosynthesis is adapted to perform in a spectrum range of solar radiation. However, an increase of solar UV radiation, caused by the depletion of the stratospheric ozone layer may result in cell damage, that it can be avoid because of the presence of some pigments able to increase the photosynthetic rate by resonance electron transfer with Chlorophyll A [31] (Fig. 2.2).

Fig. 2.1 Relationship between light intensity (I) and rate of photosynthesis (P). 

Reproduced from Q. Béchet, A Shilton, B Guieysse, Modeling the effects of light and temperature on algae growth: State of the art and critical assessment for productivity prediction during outdoor cultivation, Biotechnology Advances 31 (2013) 1648–1663.

Anyway microalgae have physiological strategies to cope with